Electricity: conductors and insulators – Conduits – cables or conductors – Preformed panel circuit arrangement
Reexamination Certificate
2001-06-14
2003-03-11
Paladini, Albert W. (Department: 2827)
Electricity: conductors and insulators
Conduits, cables or conductors
Preformed panel circuit arrangement
C174S262000, C174S266000, C174S264000, C361S793000
Reexamination Certificate
active
06531661
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a multilayer printed circuit board of the type which comprises a base member, at least one inner buildup layer formed on the base member, and an outer buildup layer formed on the inner buildup layer for mounting electronic components. The present invention also relates to a method of making such a multilayer printed circuit board.
2. Description of the Related Art
FIG. 3
illustrates an example of prior-art multilayer printed circuit board. The illustrated multilayer printed circuit board Y includes a core member
70
having a first surface
70
A and a second surface
70
B. The first surface
70
A is formed with a first base wiring pattern
70
a
, whereas the second surface
70
B is formed with a second base wiring pattern
70
b
. Two buildup layers
71
,
73
are disposed on the first surface
70
A, and other two buildup layers
72
,
74
are disposed on the second surface
70
B. Each of the buildup layers
71
~
74
as a surface
71
A,
72
A,
73
A,
74
A formed with a buildup wiring pattern
71
a
,
72
a
,
73
a
,
74
a.
The base member
70
is formed with a via hole
8
A in which conductor portion
9
A is provided. The first base wiring pattern
70
a
and the second base wiring pattern
70
b
are electrically connected to each other through the conductor portion
9
A. Similarly, the buildup layers
71
~
74
are formed with via holes
8
B~
8
H respectively provided with conductor portions
9
B~
9
H, through which the base wiring patterns
70
a
,
70
b
and the buildup wiring patterns
71
a
~
74
a
are electrically connected. Various kinds of electronic components (not shown) may be mounted on the outermost buildup layers
73
,
74
of the multilayer printed circuit board Y.
The above-described multilayer printed circuit board Y may be manufactured through the successive steps shown in FIGS.
4
A~
4
L.
First, as shown in
FIG. 4A
, a base member
70
is prepared which has a first surface
70
A and a second surface
70
B respectively formed with conductor layers
70
a
′,
70
b
′ made of copper for example. Then, as shown in
FIG. 4B
, a via hole
8
A is formed in the base member
70
by drilling for example. Subsequently, as shown in
FIG. 4C
, a conductor portion
9
A is formed in the via hole
8
A by electroless plating for example. After that, the conductor layers
70
a
′,
70
b
′ are subjected to etching, thereby providing base wiring patterns
70
a
,
70
b
, as shown in FIG.
4
D.
Then, as shown in
FIG. 4E
, buildup layers
71
,
72
each having a surface
71
A,
72
A formed with a conductor layer
71
a
′,
72
a
′, are bonded to the first and the second surfaces
70
A,
70
B of the core member
70
, respectively. Subsequently, in a manner similar to the foregoing, via holes
8
B,
8
C,
8
D are formed as shown in
FIG. 4F
, conductor portion
9
B,
9
C,
9
D are formed as shown in
FIG. 4G
, and buildup wiring pattern
71
a
,
72
a
are formed as shown in FIG.
4
H. Thus, buildup wiring patterns
71
a
,
72
a
and the base wiring patterns
70
a
,
70
b
are electrically connected through the conductor portions
9
B~
9
D. Then, similarly to the above, buildup layers
73
,
74
are laminated, and via holes
8
E,
8
F,
8
G,
8
H, conductor portions
9
E,
9
F
9
G,
9
H, and buildup wiring pattern
73
a
,
74
a
are formed, as shown in FIGS.
4
I~
4
L.
In the above-described multilayer printed circuit board Y, all of the buildup layers
71
~
74
are formed of a same material. For example, for providing a light multilayer printed circuit board Y, the buildup layers
71
~
74
maybe formed of a resin coated copper foil (RCC foil). On the other hand, for providing a multilayer printed circuit board Y having a high rigidity (flexural rigidity), the buildup layers
71
~
74
may be formed of a resin reinforced by a glass fiber such as a glass epoxy resin.
However, since the light multilayer printed circuit board Y formed of a RCC foil does not have a sufficient rigidity, it may warp when electronic components are mounted on the buildup wiring patterns
73
a
,
74
a
. Thus, it may be impossible to appropriately mount electronic components on such a light multilayer printed circuit board Y.
On the other hand, the rigid multilayer printed circuit board Y formed of a resin reinforced by a glass fiber has a disadvantageously large weight. Further, it is difficult to form via holes
8
A~
8
H by laser beam application in such a rigid multilayer printed circuit board.
Moreover, the via holes
8
A~
8
H formed by laser beam application generally have a diameter of 30~200 &mgr;m, and it is difficult to fill the via holes with the conductive material by electroless plating in forming the conductor portions
9
A~
9
H. Therefore, the buildup wiring patterns
73
a
,
74
a
include recesses at the via holes
8
E~
8
H where electronic components cannot be mounted. As a result, there exists a great limitation on the mounting positions of electronic components. To solve this problem, the via holes need to be filled with a conductor paste for example, which is troublesome. Further, the mounting of electronic components on the via holes filled with a conductor paste is not preferable in view of the conduction reliability of the electronic components.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide a light but yet rigid multilayer printed circuit board on which electronic components can be appropriately mounted.
Another object of the present invention is to provide a multilayer printed circuit board which can be made at a relatively low cost.
A further object of the present invention is to provide a method for conveniently making such a multilayer printed circuit board.
In accordance with a first aspect of the present invention, there is provided a multilayer printed circuit board comprising: a base member provided with a base wiring pattern formed on at least one surface thereof; at least one inner buildup layer laminated on said at least one surface of the base member and having a surface formed with an inner buildup wiring pattern, the inner buildup wiring pattern being electrically connected to the base wiring pattern through at least one via formed in said at least one inner buildup layer; and an outer buildup layer laminated on said surface of said at least one inner buildup layer and having a surface formed with an outer buildup wiring pattern, the outer buildup wiring pattern being electrically connected to the inner wiring pattern through at least one via formed in the outer buildup layer; wherein said at least one inner buildup layer is made of a resin material which is not reinforced by glass fibers, the outer buildup layer being made of a resin material reinforced by glass fibers.
With such a structure, the multilayer printed circuit board has a high rigidity and is unlikely to warp because the outer buildup layer is formed of a resin material reinforced by glass fibers. As a result, it is possible to appropriately mount electronic components on the board.
On the other hand, the inner buildup layer is formed of a resin material which is not reinforced by glass fibers. Therefore, it is possible to realize a weight reduction of the multilayer printed circuit board as a whole.
In the above-described structure, two or more inner buildup layers may be interposed between the outer buildup layer and the base member. In such a case, at least one of the inner buildup layers needs to be made of a resin material which is not reinforced by glass fibers, though it is more preferable if all of the inner buildup layers are made of such a material.
Preferably, the inner buildup layer may be made of a thermosetting resin such as phenolic resin, epoxy resin or polyimide resin. On the other hand, the outer buildup layer may be formed of a resin material obtained by reinforcing the above-described thermosetting resin by glass fibers. The glass fibers may be in the form of a plain-woven glass cloth or a nonwoven fabric.
The base member may be made o
Arai Keiji
Iijima Kazuhiko
Maezawa Naoto
Uchikawa Katsumi
Alcala José H.
Armstrong Westerman & Hattori, LLP
Fujitsu Limited
Paladini Albert W.
LandOfFree
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